I've not missed the point
although it is possible that I did not make it clear enough. MS should not be the only software company allowed to provide keys to be installed in UEFI as part of anti-monopoly legislation.
As long as there is one key in the UEFI to allow grub to be signed by a responsible company, then this is all that is needed, and this need key not be 'owned' by MS. Once you have a signed Grub, it is not necessary to sign all Linux kernels separately. So all it takes is for RedHat, Canonical, IBM or Google to apply for and hopefully be granted the right to add a key, provide the key to the HW manufacturers, and they would be able to provide a signed Grub image for the rest of the community. I'm sure that most HW vendors would consider adding a single non-MS key if it was provided by a reputable company - that is unless MS use their market power to dominate the HW manufacturers.
As a matter of interest, there used to be a mechanism of booting other code using what was called a 'chain-loader' that would run from DOS (it's that old) and overlay DOS with another OS. I know that Windows is a different beast and is much more secure, and there would still be the 'Windows Tax' to pay, but this may be another way around this type of issue.
I think that MS would be in for a serious anti-competitive lawsuit in the US if they prevented another software vendor from being able to have a key included in the UEFI. That would effectively mean that they would have a monopoly on all PCs sold, even if there was a way to add additional keys.